Maxima Function
idiff (expr, v_1, [n_1, [v_2, n_2] ...])
Indicial differentiation. Unlike diff, which differentiates
with respect to an independent variable, idiff) can be used
to differentiate with respect to a coordinate. For an indexed object,
this amounts to appending the v_i as derivative indices.
Subsequently, derivative indices will be sorted, unless iframe_flag
is set to true.
idiff can also differentiate the determinant of the metric
tensor. Thus, if imetric has been bound to G then
idiff(determinant(g),k) will return
2*determinant(g)*ichr2([%i,k],[%i]) where the dummy index %i
is chosen appropriately.